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Immunologic and Physical Characterization of Human Chorionic Gonadotropin and Its Subunits in Cultures of Human Malignant Trophoblast

Department of Gynecology and Obstetrics, Medical College of Wisconsin, 8700 W. Wisconsin Avenue Milwaukee, Wisconsin 53226

Culture fluids and cell homogenates from cultures of BeWo human malignant trophoblast cells were examined for the presence of chorionic gonadotropin (hCG) and its subunits by gel filtration on a calibrated Sephadex G-200 column. Culture fluids, cell homogenates, and gel filtration eluates were radioimmunoassayed in homologous hCG, hCG, and hCGβ assays.

The gel filtration pattern from the culture fluid consisted of 3 discrete antigenie peaks, including hCG and hCGβ of normal size and hCG of apparently larger than normal size. There was approximately twice as much hCG as hCGβ or hCG in the culture fluid. The gel filtration profile from the cell homogenate consisted mainly of a broad peak of hCGβ but only small amounts of hCG and hCG. The major hCGβ and hCG peaks were of apparently smaller molecular weight than highly purified hCGβ and hCG standards, respectively. The dose-response behavior of trophoblast cell homogenate in the homologous radioimmunoassays for hCG, hCG, and hCGβ provided additional evidence that hCGβ was the predominant species in the cells.

Incubation of cells with 1 mM dibutyryl cyclic AMP plus 1 mM theophylline (dbT) stimulated the secretion of hCG and hCGβ of normal size, and of the large form of hCG. The gel filtration profile of stimulated cell homogenates consisted predominantly of a small molecular weight form of hCGβ.

It was concluded that the bulk of the hCG in the cell is present in the form of its subunits, and that incubation with dbT stimulates the production of both subunits in addition to hCG.

Supported by Grant Number CA 14232 awarded by The National Cancer Institute, DHEW.

Received April 23, 1976.